The invention relates to a device for blow moulding of thermoplastic material, which has a blow mould consisting of at least two blow mould elements, with this blow mould having an interior space for the purpose of moulding a container, whereby the blow mould elements are arranged within the area of pivotally seated mould carriers.
Such devices are used in the area of rotationally driven blow wheels as well as in the area of stationary equipment. With the help of the blow mould, containers are blow moulded, for example from premoulds, that are manufactured out of a polyethylene terephthalate in an injection moulding process, with these containers being suited to holding beverages or other products.
In the devices used in the past, the design implementations for executing opening and closing movements have not met all the requirements for an uncomplicated design, a long life, and a low-cost production process.
Therefore, the object of this invention is to improve a device of the type mentioned above so as to create an uncomplicated mechanical design, providing a simple operating system, and to increase operating safety.
This object of the invention is accomplished in that the mould carriers are mounted onto a shaft, that a locking mechanism is installed in the area of the mould-carrier ends that are aligned opposite to the shaft, and that the mould carriers in the area of their extension opposite to the locking device rise above the shaft with their operating arms, which can be rotated and are connected via coupling levers to a regulating element, which is essentially mounted in the direction of a center line of the blow mould.
Because the mould carriers are being mounted on the shaft, a course of strain lines occurs through the shaft in a closed state. This situation creates favorable force inputs. Furthermore, additional locking mechanisms in the area of the mould-carrier ends opposite the shaft can be dispensed with. With the help of the locking mechanism in the area of the ends opposite the shaft, a mechanical connection of the mould carriers in a closed state is created. The operating arms allow for movement of the mould carriers according to the operating principles of a pair of scissors. Because of the connection of the adjusting element via the linking lever with the operating arms, it is possible to convert a linear motion in the direction of the center line of the blow mould into a closing motion without requiring an extensive mechanism for this process. The operation of the mould carriers is thus a purely mechanical process, so that at any point in operation an exactly defined positioning is given. Therefore in exceptional situations, at any point in time a termination of the respective course of motion and a locking of the moved elements in the respective position is possible. This results in a considerable reduction of the risk of accidents.
A preferred embodiment of this invention provides for the adjusting element being designed as a roller, which is positioned by a linking lever in the direction of the center line, which lever is connected to a shaft in the area of an end opposite to the roller. This embodiment allows in a simple fashion for the alignment of the operating elements at a given distance from the mould carriers and for the providing of a control system either above or below the mould carrier. This increases the design options for aligning the device within the area of a blow mould machine.
Another preferred embodiment provides for the alignment of the linking lever and the coupling levers in such fashion as to effect a selflocking in an opened position of the mould carrier. This selflocking mechanism reduces considerably the accident risks due to accidental mould closing motions. In particular it permits an active controlling of the adjusting element only when actual changes in positioning are to be effected. This also results in a simplified mechanical design.
According to another preferred embodiment, at least one of the blow mould elements is arranged so that it can be held in place relative to a mould carrier. Because of this fastenable arrangement it is possible to achieve a prestress on the blow mould elements after closing of the mould carrier and activation of the locking mechanism, which prevents the formation of cracks during expansion of the thermoplastic premould under pressure. This allows for the manufacture of containers of precisely specified dimensions, whose outside shapes are free from crack formations that could impair their esthetic appearance.
Other particulars of the present invention are illustrated in the following detailed description and attached drawings, which illustrate one preferred embodiment of the invention by way of example.